The work of many investigators has demonstrated the fact that nitrate nitrogen disappears from soils to which organic materials of a high carbon-nitrogen ratio have been added. Doryland in 1916 claimed that soils have a definite nitrate consuming power and that additions of organic matter such as straw, dextrose, or other soluble sugars stimulated the disappearance of the nitrates. He attributed this disappearance to the fact that the nitrates were assimilated by microorganisms but not lost from the soil

Pendleton, Ray A.

Smith, Frederick B.

English

Name not available

Studies on Methods of Measuring the Nitrate Assimilating Power of Soils

University of Northern Iowa

Proceedings of the Iowa Academy of Science Volume 36 Annual Issue Article 10 1929 Studies on Methods of Measuring the Nitrate Assimilating Power of Soils Ray A. Pendleton Iowa State College Frederick B. Smith Iowa State College Copyright ©1929 Iowa Academy of Science, Inc. Follow this and additional works at: https://scholarworks.uni.edu/pias Recommended Citation Pendleton, Ray A. and Smith, Frederick B. (1929) "Studies on Methods of Measuring the Nitrate Assimilating Power of Soils," Proceedings of the Iowa Academy of Science, 36(1), 75-78. Available at: https://scholarworks.uni.edu/pias/vol36/iss1/10 This Research is brought to you for free and open access by the Iowa Academy of Science at UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academy of Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu. STUDIES ON METHODS OF MEASURING THE NI-TRATE ASSIMILATING POWER OF SOILS RAY A. PENDLE'i'ON AND FREDERICK B. SMITH 1 The work of many investigators has demonstrated the fact that nitrate nitrogen disappears from soils to which organic materials of a high carbon-nitrogen ratio have been 1added. Doryland 2 in 1916 claitned that soils have a definite nitrate consuming power and that additions of organic matter such as straw, dextrose, or other soluble sugars stimulated the disappearance of the nitrates. He attributed this disappearance to the fact that the nitrates were assimilated by microorganisms but not lost from the soil. The fact 1that microorganisms thus enter into competition with the higher plants for soil nitrates makes it desimble to study the factors involved with a view to ascertaining whether or not they can be controlled to any extent. Assuming that soils have a definite nitrate consuming power which can be altered by different treat-ments, it is conceivable that some method might be devised where-by this consuming power can be measured, at least under specific conditions. Murray 3 in his studies of the effect of s'traw on soils, in 1921 :attempted to measure their nitrate assimilating capacity. He added finely chopped straw in amounts of 0.1 to 5.0 percent and 50 mgm. of sodium nitrate to 100 grams of soil in tumblers. He found that 1.0 percent of straw caused a loss of soil nitrates but his incubation period was rather long and this makes compari-sons with the work reported in this paper rather difficult. Smith 4 in 1928 reported results using a soil culture method for determining the nitrate assimilating power of :a soil. In this paper some addi-tional data are presented along the same line. The nitrate content of a soil at any time is undoubtedly the resultant of a number of different microbiological processes. Chief among these activities :are nitrification, which tends to increase the nitrate content of the soil, and nitrate assimilation, which tends to 1 The authors express their appreciation of the reading and correction of the manu-script by Dr. P. E. Brown. 2 D<>ryland, C. J. T. 1916. The Influence of Energy Material upon the Relation of Soil Microorganisms to Soluble Plant Food. N. D. Agr. Exp. Sta. Bui. 116: 319-401. 3 Murray, T. J. 1921. The Effect of Straw on the Biological Soil Processes. Soil Sci. 12: 233·259. . ·4 Smith, F. B. 1928. The Nitrate Assimilating Power of the Soil and Some Nitrate Assimilating Soil Bacteria. Proc. Iowa Acad. Sci. V. 35. (In press.) 75 1Pendleton and Smith: Studies on Methods of Measuring the Nitrate Assimilating Power ofPublished by UNI ScholarWorks, 192916 IOWA ACADEMY OF SCIENCE decrease the nitrate content. In order to measure the nitrate assim-ilating power of a soil with any degree of accuracy, it is very desirable to devise some means whereby the o:ther processes in-volved can be kept at a minimum. Many investigators have found that cellulose and certain soluble carbonaceous organic materials arrested or inhibited nitrification in solution 1and soil cultures. An :attempt was made in the following experiments to retard nitrification by additions of straw, dextrose and starch. 100 gram equivalents of air dry soil were weighed out into tumblers suffi-cient for 4 sets of 40 tumblers each. Set 1 was left untreated, to set 2 was added 2 percent of finely ground straw, to set 3, z' percent of dextrose, and to set 4, 2 percent of starch. These materials were all well mixed with the soil. Each set was then divided into 4 like groups of ten tumblers each to be incubated 1, 2, 3 and 4 weeks respectively. Each group of 10 tumblers was then divided into 5 series to which were added 0.0, 5.0, 10.0, 15.0, and 20.0 mgm. of nitrate nitrogen so that all treatments were made in duplicate. These were all.incubated at optimum moisture and temperature for the allotted time and the nitrates determined by the phenol-disul-phonic acid method. The amount of nitrate assimilated w:as cal-culated as the difference between the amount remaining and the amount added plus the original nitrate content of the soil. In cases where a neg;ative :assimilation is indicated, there was an increase in the amount of nitrates, due to nitrification. Before this work was completed, a 11ew set of tests was prepared using a one week incubation period. The same treatments were followed :as above except that a soluble form of starch w:as sub-stituted for the insoluble form. The data obtained from this latter group are given in table I. The data for ihe original four groups are given in tables II, III, IV and V. It was hoped that an analysis of the data obtained would pro-vide an :answer for the following questions which have arisen during this study: ( 1) How long should the incubation period be Table I -Milligrams Nitrate-N. Assimilated per 100 Grams Dry Soil After One Week* TR!tATMBKT SorL Sorr<+2% Sou"+2% Sor1+2% ALONE STRAW Dl\XTROSF. SOLUBLE'. STARCH No treatment -1.85 1.28 1.28 1.28--5.00 mgms. l\'Os-l\'. -0.39 6.28 I 6.28 6.28 10.00 mgms. N Oa-N. -0.34 10.39 9.44 11.28 15.00 mgms. NOa-l\'. 0.93 10.60 13.58 16.28 20.00 mgms. NOs-N. 5.18 10.63 9.38 17.08 ·-*Soil contained 1.28 mgm. NO:JN. per 100 gm. soil in beginning. 2Proceedings of the Iowa Academy of Science, Vol. 36 [1929], No. 1, Art. 10https://scholarworks.uni.edu/pias/vol36/iss1/10NITRATE ASSIMILATING POWER OF SOILS 77 Table II -Milligrams Nitrate-N. Assimilated After One Week, Per 100 Grams Dry Soil * TREATMEC\'T So IL SorL+2% DRY Son+2% SorL+2% ALO::iE OA'l'S STRAW DEX'l'ROSE STARCH No treatment -8.88 1.28 1.28 . 1.28 5.00 mgms. N03-N. -10.12 6.28 6.28 5.23 10.00 mgms. NO.-N. 0.93 9.43 11.28 5.34 15.00mgms. NO,-N. 2.03 12.05 16.28 6.13 20.00 mgms. KO,-N. 2.38 12.18 17.67 9.30 - --- -----*Soil contained 1.28 mgms. ~03N. per 100 gms. dry soil in the beginning. Table III -Milligrams Nitrate-N. Assimilated Per 100 Grams Dry Soil After Two Weeks ==============:c--:==~= I SorL_I __ TREATMEKT ALONE No treatment -1.21 ' --SOIL+ 2% DRYI OATS STRAW 1.28 5.00 mgms. N03-N. -0.86 10.00mgrns. NOa-N. -1.22 15.00mgrns. NOa-N.. 0.58 20.00 mgrns. NO,-N. ~ _ 6.28 11.00 13.14 14.66 SorL+2% So1L+2% DEXTROSE STARCH 1.28 1.28 6.28 6.28 11.28 9.08 14.00 7.11 19.24 12.26 Table IV -Milligrams Nitrate-N. Assimilated Per 100 Grams Dry Soil After Three W ee!?s TREA1'MEN1' Son, SorL+2% DRY So1L+2% SorL+2% Ar.ONE OA'I'S S'I'RAW DEX'l'ROSE STARCH :t\ o treatment ~ 1.28 1.28 1.28 5.00 rngms. NOs-N. 0.23 6.28 6.28 6.28 10.00 mgms. NOs-N. 0.18 11.28 11.28 11.28 15.00 mgrns. NOs-N. -1.36 13.72 14.53 10.85 20.00mgms. NO,-N. 4.83 15.73 18.00 10.88 Table V -Milligrams Nitrate-N. Assimilated Per 100 Grams Dry Soil Aftc1· Four Weeks -TREATMEKT SOIL SOIL+ Z:% DRY/ SorL+2'% So1L+2% Ar,o:fE OA'l'S S1'RAW DEX'l'ROSE S'l'ARCH No treatment -1.55 1.28 1.28 1.28 5.00 mgms. NOrN. 0.18 6.28 6.28 6.28 10.00mgms. NO,-N. -0.52 11.28 11.00 11.28 15.00 rngms. NO.-N. 1.08 14.34 13.92 13.53 20.00 rngrns. NO,-N. 3.28 16.20 16.08 13.42 extended in order to get the most consistent results? (2) How much nitrate should be added? ( 3) Should some form of organic matter be added and if so, what form is best suited to the study? The data in all cases where no organic ma·tter was added are euatic and difficult of interpretation. These data are the most in-consistent of all obtained and indicate that incubation of the soil alone is not as desirable a method of procedure as incubation with some organic matter added. In practically all cases with organic matter added, where only 5 mgm. of nitrnte were used, this nitrate was all assimilated in one week's incubation period. From this it can be concluded that either a shorter incubation period than one 3Pendleton and Smith: Studies on Methods of Measuring the Nitrate Assimilating Power ofPublished by UNI ScholarWorks, 192978 IOWA ACADEMY OF SCIENCE week or a larger amount than 5 mgm. of nitrate is necessary for good results. In most cases with the 3 or 4 weeks incubation period, all the nitrate added up to 10 mgm. was assimilated. This indicated that if only 10 mgm. nitrate are to be added" then a very short incubation period should be used. 'Where a soluble form of organic n1atter was added, the nitrate assimilating power appeared to be somewhat higher than where an insoluble form of organic matter was used. Yet the consistency of the results obtained from the straw indicates that the results secured from this method might be just as useful for comparative purposes as the results secured when a more soluble form of or-ganic matter was used. A study of the tables indicates that ·the amount of nitrate assirnitated may be increased in three different ways: by using a very soluble form of organic matter, such as soluble starch, by increasing the amount of nitrate added, or by extending the incubation period. As stated above there may be no advantage in using the more soluble form of organic matter. vVhere the incubation period was limited to one or two weeks, additions of 20 mgm. of nitrates did not show much greater assimilation than 15 mgm. additions. From this it might be concluded that for this type of soil, 15 mgm. per 100 grams o.f soil is sufficient. Although the amount of nitrates assimilated is slightly increased by extend-ing the incubation period to 3 and 4 weeks, it is not increased in proportion to the extra time. The increased opportunity for the interference of other factors with the longer time would seem to make it desirable to limit the incubation period to not over two weeks, and there is a possibility that less than one week would be prefer:able. It is admitted that the results so far obtained are of interest mainly as being indicative of certain tendencies which need further verification. They do show, however, quite conclusively that soils have a definite nitrate assimilating power which may be favored by additions of organic matter. The data also indicate that it may be possible to measure this nitrate assimilating power and correlate it with other microbiological activities. It is planned to continue the work with a view to supplementing the information already obtained. Iow A STATE CoLLI\.GE, AMES, IowA.4Proceedings of the Iowa Academy of Science, Vol. 36 [1929], No. 1, Art. 10https://scholarworks.uni.edu/pias/vol36/iss1/10

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Studies on Methods of Measuring the Nitrate Assimilating Power of Soils

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